PHYSICAL MODEL OF DIURNAL HEATING IN THE VICINITY OF A 2-DIMENSIONAL RIDGE

Citation
Rr. Chen et al., PHYSICAL MODEL OF DIURNAL HEATING IN THE VICINITY OF A 2-DIMENSIONAL RIDGE, Journal of the atmospheric sciences, 53(1), 1996, pp. 62-85
Citations number
38
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Metereology & Atmospheric Sciences
Journal title
ISSN journal
0022-4928
Volume
53
Issue
1
Year of publication
1996
Pages
62 - 85
Database
ISI
SICI code
0022-4928(1996)53:1<62:PMODHI>2.0.ZU;2-O
Abstract
Laboratory experiments were conducted to simulate the diurnal heating- cooling cycle in the vicinity of a ridge of constant cross section. In the model the fluid is a water solution stratified with salt to simul ate the background stratification of the atmosphere. The flow is drive n by recirculating water of a controlled temperature beneath the model ; the model surface temperature is thus varied in a specified way to s imulate the surface heating by solar insolation during the daytime hou rs and surface cooling by radiation during the nighttime. The pertinen t similarity parameters are shown to be G(c) for daytime convective fl ow and G(d) for nocturnal how; here G(c) = H-b/H-c, G(d) = H-b/H-d, wh ere H-b is the mountain height, H-c the neutral buoyancy height of fre e convection, and H-d the characteristic thickness of the nighttime dr ainage Row. The model demonstrates some of the principal features of t hermally driven mountain circulations, including daytime upslope winds and nocturnal downslope drainage flows. The spatial and temporal stru ctures of these motion fields are delineated, with the following being among the most important observations: (i) during the daytime, the up slope convective how in the vicinity of the mountain tends to suppress convective turbulence over the horizontal plains; (ii) during the ear ly evening, horizontal jets, with the principal one directed toward th e mountain, develop above the mountain surface, and vortices in the ve rtical cross section develop both above and below the jets, following the collapse of the convective motion over the mountain; and (iii) in the evening, a downslope drainage Row is initiated following the estab lishment of a vertical vortex on the mountain slope and under the jet. Quantitative experimental observations are made, which demonstrate th e variation of various how observables with the pertinent similarity p arameters. These results are applied to the atmosphere following simil arity relations between the physical model and the atmosphere. The pre dicted characteristic speeds and length scales of the daytime upslope flow and the nocturnal drainage flow for typical atmospheric parameter s are in reasonable agreement with limited field observations.